What value does theabout:config item view_source.editor.external need to open into vi text editor in the terminal? /bin/vi/ is not enough - after putting that value in, browsing to view-source:www.w3.org (note that here on this page the link fails because the phone sends the string to a search engine instead of using the view-source protocol prefix properly) still shows the page source in the browser, instead of vi in fingerterm.

Does it take a command something like /usr/bin/xdg-open /usr/bin/fingerterm -x /bin/vi to get the desired result? Does a MIME type need to be defined to open fingerterm for the executable /bin/vi?